Contemporary multi-engine jet aircraft are manufactured with two, three, or four jet engines. The engines of two- and four-engine aircraft are mounted on opposite sides of the engine fuselage. The "side mounted" engines may be hung from the wings of the aircraft or, in the case of two-engine aircraft only, attached to the fuselage of the aircraft. In the case of three-engine aircraft, one of the engines is mounted in the fuselage so as to provide thrust along the fuselage axis. The remaining two engines are mounted on opposite sides of the fuselage, or on opposite wings. In order to provide symmetrical thrust, in most instances, the engines mounted on opposite sides of the fuselage of an aircraft are identical when an aircraft is fabricated. That is, even though engine type varies from airplane to airplane depending upon a customer's thrust requirements, which are dependent upon a customer's route structure, fuel utilization requirements and capital limitations, side mounted engines are identical, i.e., they are of the same type and have the same rating, when an aircraft is delivered. Usually, but not necessarily, the mid-engine of a three-engine aircraft is identical to the side mounted engines.
When an engine requires replacement, it is replaced as quickly as possible to minimize aircraft down time. In order to achieve this result, engines are replaced with the most readily available engine having a thrust rating that is appropriate for the aircraft considering current needs and/or route structure. Because modern jet engines can provide a variety of thrust levels with different fuel controllers, replacement engines are not always identical to the engine being replaced. Occasionally, replacement engines are different in thrust and dynamic performance than the engine being replaced. When the engine being replaced is a side mounted engine, such replacement results in an engine mismatch. In the past, when a replacement side mounted engine does not match the remaining side mounted engine, the automatic throttle control system of the aircraft was disabled because current automatic throttle control systems use a common control channel to control the thrust produced by all the engines of a jet aircraft. Obviously, different side mounted engines are likely to produce asymmetrical thrust when controlled by a common thrust control signal.
Under current operating rules of government regulatory agencies (FAA, CAA, etc.), certain automatic procedures, such as automatic landings, are prohibited when an automatic throttle control system is disabled. This may limit the use and cause delays of such an aircraft. More specifically, the operating procedures followed by aircraft with automatic throttle control systems are established by various government agencies. In certain instances, an automatic throttle control system is required for speed control while an aircraft is performing an automatic landing. As noted above, in the pas, automatic throttle control systems have been disabled on aircraft with unmatched side-mounted engines, i.e., aircraft with side-mounted engines having differing thrust characteristics. As a result, automatic landing procedures are unavailable to pilots operating such aircraft.
This invention is directed to providing an automatic throttle control system for controlling the engines of multi-engine jet aircraft having unmatched side-mounted jet engines, i.e., jet engines with different thrust ratings and dynamic characteristics. Thus, the invention is directed to eliminating engine intermixing as an item that prohibits the use of an automatic throttle control system by pilots. This is especially important to aircraft operators operating under rules that require an automatic throttle control system to control speed during an automatic landing.